This invention relates to educational demonstrations, and more specifically to the apparatus of a variable torque pulley which is used to demonstrate the principles of torque and the inverse square law.
Essentially the magnitude of all the forces at work, which we experience in our macroscopic world, vary with distance according to the inverse square law, such as the gravitational force, the magnetic force, and the electric force. Some examples of this are the following: The gravitational force between any two objects varies inversely with the square of their separation. The magnetic force between a magnet and a piece of iron varies inversely with the square of their separation. The electromagnetic force that binds atoms and molecules together is an electric force between charged elementary particles such as protons and electrons. This force varies as the inverse square of the separation of the particles. These concepts are abstract and difficult to understand, for it is not easy for most students to visualize this force distance relationship. This invention solves that problem by providing a physical demonstration that students can touch feel and experience for themselves to help them better understand the laws of the natural world.
In accordance with the present invention a variable torque pulley consists of a rigid overlapping spiral shape member and a rigid circular member. The circular member is attached to the spiral shaped member as one integral piece, each incorporating a groove around the perimeter to act as a guide for a length of string. The circular member acts as a pulley and the spiral shape member acts as a lever. The variable torque pulley rotates in a circular fashion pivoting on an axle about its center. String is used with the circular member to rotate the apparatus. String is also used with the spiral shape member for the hanging of a weight. The axle acts as the fulcrum for the spiral shape member. The shape of the spiral is important because as the variable torque pulley rotates, the weight moves toward the fulcrum and the torque drops off in harmony with the inverse square law. The invention helps students to better understand the concept of the inverse square law by providing a dynamic and tangible demonstration. The demonstration is interactive; such that it allows the student to feel the gravitational force of an object, in this case a weight, change with distance according to the inverse square law. Furthermore the invention allows students to visualize the concept of torque as a vector product consisting of both a force and a length of lever arm as the length of the arm changes. After finishing the experiment, the student can plot what he or she is visualizing and gain important practice with his or her graphing skills.